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Commit 3e24b19d authored by Vladimir Davydov's avatar Vladimir Davydov Committed by Linus Torvalds
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Documentation: cgroup: add memory.swap.{current,max} description 



The rationale of separate swap counter is given by Johannes Weiner.

Signed-off-by: default avatarVladimir Davydov <vdavydov@virtuozzo.com>
Acked-by: default avatarJohannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@kernel.org>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 5ccc5aba

Documentation/cgroup-v2.txt

+33 −0
Original line number Diff line number Diff line
@@ -819,6 +819,22 @@ PAGE_SIZE multiple when read back. 
		the cgroup.  This may not exactly match the number of

		processes killed but should generally be close.



  memory.swap.current



	A read-only single value file which exists on non-root

	cgroups.



	The total amount of swap currently being used by the cgroup

	and its descendants.



  memory.swap.max



	A read-write single value file which exists on non-root

	cgroups.  The default is "max".



	Swap usage hard limit.  If a cgroup's swap usage reaches this

	limit, anonymous meomry of the cgroup will not be swapped out.





5-2-2. General Usage
@@ -1291,3 +1307,20 @@ allocation from the slack available in other groups or the rest of the 
system than killing the group.  Otherwise, memory.max is there to

limit this type of spillover and ultimately contain buggy or even

malicious applications.



The combined memory+swap accounting and limiting is replaced by real

control over swap space.



The main argument for a combined memory+swap facility in the original

cgroup design was that global or parental pressure would always be

able to swap all anonymous memory of a child group, regardless of the

child's own (possibly untrusted) configuration.  However, untrusted

groups can sabotage swapping by other means - such as referencing its

anonymous memory in a tight loop - and an admin can not assume full

swappability when overcommitting untrusted jobs.



For trusted jobs, on the other hand, a combined counter is not an

intuitive userspace interface, and it flies in the face of the idea

that cgroup controllers should account and limit specific physical

resources.  Swap space is a resource like all others in the system,

and that's why unified hierarchy allows distributing it separately.